<!DOCTYPE html>
<html lang="zh-CN">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            width: 100%;
            height: 100%;

        }

        button {
            margin: 20px 100px;
            padding: 10px 20px;

        }
    </style>
</head>

<body style="background-color: white;">
    <button class="btn">点击更换BOOY皮肤(白->红->绿->蓝->黑->白)</button>
    <script>
        var body = document.body;
        var btn = document.querySelector('button')

        btn.onclick = function () {
            switch (body.style.backgroundColor) {
                case 'white':
                    body.style.backgroundColor = 'red'
                    break
                case 'red':
                    body.style.backgroundColor = 'green'
                    break
                case 'green':
                    body.style.backgroundColor = 'blue'
                    break
                case 'blue':
                    body.style.backgroundColor = 'black'
                    break
                case 'black':
                    body.style.backgroundColor = 'white'
                    break
            }
        }
    </script>
</body>

</html>